Method of heat treating



y 5, 1941- F. s. DENNEEN ET AL 2,240,494

METHOD OF HEAT TREATING Original Filed March 29, 1934 INVENTORS Sa M w l Patented May 6, 1941- I v a 2,240,494

UNITED STATES PATENT OFFICE METHOD OF HEAT TREATING Francis S. Denneen, Cleveland, William C. Dunn, Shaker Heights, and Courtney N. Mitchell, Strong'sville, Ohio, asslgnors to The Ohio Crankshaft Company, Cleveland, Ohio, a corporation of Ohio Original applications March 29, 1934, Serial No.

718,002 and Serial No. 718,003. Divided and glggssapplicatlon November 10, 1938, Serial No.

3 Claims. (Cl. 148-21) This application is a division of our co-pending through an inductor and a crankshaft pin havcases Serial Nos. 718,002 and 718,003, filed March ing the oil passage therein plugged or filled in 29, 1934, and is directed to the art of electrically accordance with the invention.

heating metals for surface hardening and par- Referring now to the drawing, an inductor 5 ticularly tothe surface hardening of metals with 5 is provided to encircle the shaft undergoing holes and recesses therein, as oil holes and heating for hardening. This inductor lies in keyways. closely spaced relation with the shaft and by The invention relates to the surface hardenmeans of a periodically varying current passed ing by inductive or other heating followed by through the inductor there is induced in the quenching, of metal articles having in their surl0 underlying surface zone of the shaft a magnetic face various types of recesses or openings, such flux by which the said zone is heated to the as oil holes, keyways or the like. By the term desired temperature. A plurality of quench surface hardening is meant the formation of orifices 1 provide outlets from a hollow chamber a hardened surface zone only, of limited depth, 8 on the interior of the inductor and are adapted by rapidly heating said surface zone to hardening to direct quench against that portion of the shaft temperature and quenching the heated surface heated by the inductor. The quench is supplied before any substantial amount of heat has passed 7 with sufficient rapidity and in sumcient volume into the interior or core of the article. to efi'ectively quench the zone and retain the The normal distribution of induced current and desired metallurgical characteristics sought quenching fluid, when said articles are being after. Such apparatus and method by which the surface hardened, is such as to cause extreme same is employed are best shown in the parent local hardness and a tendency of the metal to cases, of which this is a division. crack at the edges of their recesses or openings, The pin or. shaft 80 is provided with an oil and the object of the present invention is to prehole I 2 opening into the cylindrical surface to vent or retard the penetration at these edges 95 behardened. In ordertoprevent the penetration of both the heat and the quenching action, so of heat and retard the penetration of quenching that the surface structure around the recess or fluid to the edges of the hole l2 adjacent said opening will not differ appreciably from that at surface, and thereby prevent extreme local hardother parts of the hardened surface. ness and tendency for the metal to crack at the According to the invention, in the surface said edges, one or both ends of the said oil hole hardening, by inductive or other heating and B2 are closed by a plug or fill n during the quenching, of a metal article having a recess or heating and quenching periods. A solid plug opening in its surface, said recess or opening id, as shown at the lower end of the hole, may is partially or completely closed by a plug or be employed, preferably made of a low-carbon filling during the heating and quenching periods. non-hardening steel; or a plastic or semi-plastic The recess or opening may be so closed either filling l6, as shown in the upper end of the hole, by a solid plug or by a filling with a plastic or may be employed. It is desirable, however, that semi-plastic material. For inductive heating the the plug or filling should possess magnetic propplug or filling is preferably of a magnetic and erties and current-carrying ability as closelycurrent-conducting character, and it is desirable approximat hat f the m l n the Shaft 8,818 that such magnetic property and current-carrypossible. Further, it is desirable that the nature ing ability should closely approximate that of the of the material be such that, after heating and metal in the article being hardened. quenching, it will remain softer than the hard- The nature of the material of the plug or ened surface so as to permit of easy removal. filling may be such that after heating and In the case of a plastic or semi-plastic filling, quenching it will remain softer than the hardfinely divided low-carbon steel mixed with ened surface so as to permit easy removal. It asbestos, clay or some other material and a may, for example, consist of finely divided low suitable binder may be usedv to advantage. This carbon steel mixed with asbestos, clay or other mixture may be molded to shape, baked or dried, material and a suitable binder. If it is a solid and then inserted in the recess; or it may be plug, it may consist of low carbon non-hardening pressed in the recess in plastic condition.

steel. Vent passages maybe provided in the plug Since the gas in the plugged recess expands or filling or the latter may be made of a porous with heat and tends to force the plug out of character. place, it is desirable that a sufficient vent be The accompanying drawing is a sectional view provided in the plug, such as by the provision of avent passage l8 shown in the plug or filling It; or the plug or filling may be a loose fit at some point; or the plug itself may be made sufliciently porous to permit the gas to escape.

The application of the invention to other articles having any form of recess in its surface, such as a keyway or other recess, differs in no essential respect from its application to a shaft having an oil hole through it as hereinbefore described.

Other modes of applying the principle of our invention may be employed instead of the one explained, change being made as regards the means herein disclosed, provided the means stated by any of the following claims or the equivalent of such stated means be employed.

We therefore particularly point out and distinctlyclainr as our invention:

1. In a method of inductively heat treatin a surface zone of an article with a recess in the surface thereof, the steps of filling such recess only to the outer edge thereof without covering said surface with a current conducting pliable plug comprising a current conducting medium having a low carbon content and a binder, said plug being of such viscosity that it will not freely flow, causing the inductive heating current to flow through said surface zone and said plug, thereafter quenching said surface zone and then removing said plug from said recess.

2. In a method of inductively heat-treating a surface zone of an article with a recess in the surface thereof, the step of filling said recess with a plug comprising finely divided low-carbon steel and a plastic binder so that said plug terminates at the recessed side walls and leaves the surface zone uncovered, placing an inductor heating element in heating relation with said surface zone to inductively heat the same, quenching said zone and thereafter removing said plug.

3. In a method of inductively heat treating a surface zone of an article with a recess in the surface thereof, the steps of filling said recess with a plug characterized by low carbon content and permeability and electrical conductivity approximately that of the article, causing heating current to flow through said surface zone and through the plug, thereafter quenching said surface zone and then removing said plug from said recess.

WILLIAM C. DUNN. FRANCIS S. DENNEEN. COURTNEY N. MITCHELL. 

